The United States Pharmacopoeia has wisely adopted the French Metric or Decimal system of weights and measures. Consequently this system is given precedence in this book.
The Decimal system is far superior to the old Troy weights and wine measures, both in simplicity and in offering less opportunity for error. In order to acquire the advantages of the simplicity of the Metric scale one has but to consider grams, centigrams and milligrams, as respectively dollars, cents and mills; cubic centimeters as dollars, and fractions of a cubic centimeter as fractions of a dollar.
It is absurd to accurately translate or transpose the old system into the new, or the reverse, as the range of dose of every drug named in the Pharmacopoeia is far wider than the minute difference caused by transposing a given dose in one system to an approximate dose in the other. The ridiculous fractions produced by absolute equivalence are chemically correct, but pharmacallv and therapeutically unseemly. Hence the student should learn one system by itself and compute in it, and not in terms of the other. If translation is necessary, it should be free and not literal, i. e., an approximate equivalence.
In the United States solid drugs and preparations are weighed and liquid drugs and preparations are measured when written in the Metric scale, as well as when written in the old scale.
The Base Of This System Is The Meter, An Established Length, Representing One-Forty Millionth Part Of The Earth's Circumference Around The Poles, And Equivalent To 39.370432 inches.
The unit of volume is the liter, a cube having the length of its side equal to 1-10 of a meter, and equivalent to 2.056716 pints.
The unit of weight is the gramme, the weight of a cube of water at 4° C. having the length of its side equal to 1-100 of a meter, and equivalent to 15.432 grains.
For convenience of expression a smaller unit of volume and a larger unit of weight are used, namely, the cubic centimeter (1-1,000 of a liter, that is a cube having for its side 1-100 of a meter) and the kilogram (1,000 grammes), about 2 1-5 pounds. Microscopists make use of a still smaller unit of length, namely the Mikron (abbreviated by the Greek letter
or micro-millimeter, a thousandth part of a millimeter, equal to about 1-25000 of an inch.
The steps in the tables are all by a factor of 10. Those below the unit are expressed by their Latin, and those above by their Greek names, viz.: